Monday, March 7, 2011

How To Make A Custom Length Machine Screw

I needed an 8-32 x 0.760" long stainless steel machine screw recently.  A 1" long one would not work, and I could not find a 7/8" long one anywhere that I tried.  (And I'm not sure that 7/8" would have worked, anyway.)  So how to cut down such a small screw?  You can't really hold safely under a chop saw, or a band saw and even if you could, you would need to run it through a die to get the threads at the end clean.  I discovered that my lathe chuck would not hold it solidly enough centered--it is just too small. 

What I did was to drill and tap an 8-32 hole through a piece of acetal so that the screw would stick up through the top of the acetal block.  Now I could clamp the block down solidly in the vertical mill, and take repeated .010" passed across the top of a 1" long 8-32 screw until I had reduced it to the correct size.  Best of all, the process was so precise that I did not need to clean up the threads.


  1. Some of those old-school 'stakon' pliers have threaded holes that you can thread screws into and then shear them off.

    You know the pliers I mean? The ones that are used for crimping butt splices and electrical connectors.

  2. Most electrical crimper tools have the capacity to sheer small screws, say #10 and smaller. It might be a little trickier to get the exact length but I used this a lot to shorten small screws and as you can imagine, it is very quick.

  3. I have a couple of different pairs of wire crimper/stripper tools that have cut-off holes for various sized small screws in them.

    Like these:

    They work adequately well...

  4. Dear Mr. Cramer,

    Electrical pliers typically have built in bolt cutters, i.e. You screw the bolt into the pliers, thus protecting the screws, and the blade cuts the bolt. Very quick and easy.



  5. That certainly works.

    I'd have probably just taken a grinder to it, and a file for the last final bits if length was super-critical.

    And then a few seconds with a die and it's clean.

  6. I like Dremel tools with a cut-off disk for something like this if it's only a one-off. If you've got a halfway steady hand it's unlikely you'll need to even touchup the threads.

  7. Well, he did say 0.760"--what kind of tolerance are you going to achieve with your Dremel or your electrical pliers?

  8. All rather complex methods requiring major hardware. The easiest route I have found is to start by putting 3 or 4 nuts on the shaft. Align the nuts so the hex faces are even and the last nut is aligned with the length you want. In most of the cases I am doing this, that depth is about a 32nd below where the installed and tightened nut (actually generally a nylock) will end up.
    Clamp upright in a vice, or use vice-grips.
    File the excess down to the correct level. This only takes a few seconds with #10 or #8 bolts. Brass bolts are *easy*.
    Spin the bottom 2 nuts against each other and apply a wrench or the vice-grips to the bottom nut. Using a wrench, wind off the topmost nut, cleaning up the threads.
    Remove nuts.
    (I'll just let that line age right there, despite temptation!).

    Rinse, repeat as necessary.

    I end up doing this whenever I make major changes in the rigging layout on my sailboat. I don't want the bolts any longer than necessary, since they always turn hostile to either skin or sails!
    In many cases, I just file the bolt down to length, in place, across the nylock. Extraction is not that difficult as the file does not really destroy the thread.

    Hhhmmm, the capcha is 'enflogg'.

    Getting kinky are we?